Changing Planet

Absent efforts well beyond those described in the Paris Agreement—to limit warming to well below 2 degrees Celsius above pre-industrial levels and to pursue efforts to limit that increase to 1.5 degrees Celsius—climate change could pose a deadly threat to most humans by century’s end. This finding was suggested by an international group of climate science and policy experts in a pair of recently published studies.

To avoid the worst consequences of climate change, a paper published in the Proceedings of the National Academy of Sciences (PNAS) said the world would have to take aggressive measures to curtail the use of fossil fuels and emissions of short-lived climate pollutants such as methane. In addition, we would also have to extract carbon dioxide from the air and sequester it before it can be emitted.

According to the findings, which were originally published by the University of California’s Scripps Institution of Oceanography, there is a 5 percent chance of catastrophic change within roughly three decades, and a smaller chance that it would extinguish human life. It proposed two new classifications for climate change: “catastrophic,” meaning that adaptation would be difficult for most people, and “unknown,” or “existential,” meaning that adaptation would be impossible.

“There is a low probability that the change will be catastrophic,” said the study’s lead author, Veerabhadran Ramanathan, a professor of climate and atmospheric sciences at Scripps. “But you would not get on an airplane if you thought there was a 5 percent chance that it was going to crash.”

The researchers defined their proposed risk categories on the basis of guidelines established by the Intergovernmental Panel on Climate Change and previous independent studies. Even a global temperature increase limited to 1.5 degrees Celsius (2.7 degrees Farenheit)—the Paris Agreement’s aspirational goal—is categorized as “dangerous.” An increase greater than 3 degrees Celsius (5.4 degrees Farenheit) could be “catastrophic,” and an increase greater than 5 degrees Celsius (9 degrees Farenheit) could lead to “unknown” but potentially existential threats. For humans, catastrophic impacts include widespread famine and the exposure of more than 7 billion people to heat-related mortalities.

Policy and science experts, including Ramanathan, relied on the PNAS findings to compile a report on potential warming containment efforts. That report pointed to the need for greater weight on subnational government action and a sharp uptake in mature clean energy technologies—such as wind, solar, biogas, and geothermal—coupled with aggressive electrification of transportation and building energy use.

A separate analysis published in the journal Nature Geoscience says the Paris Agreement’s 1.5 Celsius aspirational goal may be more feasible than many think. It makes a fresh estimate of the necessary carbon budget, including updating measurements of the emissions and warming that have already occurred, and shows that the global carbon emissions budget that meets that goal is equivalent to 20 years of current global annual emissions. But other researchers have raised questions about the analysis—which, if correct, would have very large implications for climate policymaking. Aside from concerns about the new study’s methods and assumptions, broader questions about the definition of the carbon budget and how it should be calculated are now swirling.

“There has been no change in the United States’ position on the Paris agreement,” White House Deputy Press Secretary Lindsay Walters told CNN. “As the President has made abundantly clear, the United States is withdrawing unless we can re-enter on terms that are more favorable to our country.”

Despite the White House’s stance on the global climate accord, others are taking steps to acknowledge and, in some cases, take specific action on the issue. Republican Sen. Lindsey Graham on Tuesday told guests attending a climate change conference convened at Yale University by former Secretary of State John Kerry that he supports a carbon tax to reduce greenhouse gas emissions.

“I’m a Republican. I believe that the greenhouse effect is real, that CO2 emissions generated by man is creating our greenhouse gas effect that traps heat, and the planet is warming,” said Graham. “A price on carbon—that’s the way to go in my view.”

Sen. Graham’s reinvocation of these concepts means that there may be some ability to have conversations again about the bipartisan solution to climate change (subscription).

State and local leaders associated with the C40 Cities Climate Leadership Group—a network of megacities dedicated to addressing climate change—remain focused on faster climate action. As part of a Climate Week convening, several mayors discussed how that action falls on them now that the United States is pulling out of the Paris Agreement.

“As mayors, our responsibilities also became even clearer. It’s not enough to reach our ‘80 by 50’ goal,” said New York City Mayor Bill de Blasio, referencing New York City’s earlier commitment to cut greenhouse gases by 80 percent by midcentury, “or to go along with the fantastic goal of keeping warming to two degrees Celsius. If the U.S. government is backing away, we had to step forward.”

On Wednesday, 91 U.S. cities and Denmark unveiled a climate plan that aims to enhance cooperation among companies, governments, regions and cities in an effort to promote green growth. The initiative is dubbed Partnering for Green Growth and the Global Goals 2030. Also, North Carolina joined 14 other states in the U.S. Climate Alliance—a bipartisan group of states committed to reducing their share of greenhouse gas emissions in line with the goals that countries agreed upon as part of the Paris Agreement.

“In the absence of leadership from Washington, North Carolina is proud to join the U.S. Climate Alliance, and we remain committed to reducing pollution and protecting our environment,” said North Carolina Gov. Roy Cooper. “So much of North Carolina’s economy relies on protecting our treasured natural resources, and I’m committed to maintaining the quality of their air we breathe for generations to come.”

The report indicates that fossil fuels will continue to dominate the world energy mix, making up 77 percent of energy use in 2040, while renewables, despite growing faster than any other fuel source during the coming years, will represent just 17 percent of world energy consumption by 2040. Demand for coal will remain relatively flat with consumption projected to decline from 27 to 25 percent between 2015 and 2040.

Global natural gas consumption is seen increasing by 1.4 percent per year over the forecast period.

Meet the Author

Tim Profeta is the founding director of the Nicholas Institute for Environmental Policy Solutions. The Nicholas Institute is part of Duke University and focuses on improving environmental policy making worldwide through objective, fact-based research in the areas of climate change, the economics of limiting carbon pollution, oceans governance and coastal management, emerging environmental markets and freshwater concerns at home and abroad. In his role at the Nicholas Institute, Profeta has continued to use his experience on Capitol Hill to engage in climate change debates. His research has focused, specifically, on market-based approaches to environmental regulations—particularly energy and climate change policy. Other projects engage his expertise in environmental law and air pollution regulation under the Clean Air Act.

Post Navigation

Related Posts

About the Blog

Researchers, conservationists, and others share stories, insights and ideas about Our Changing Planet, Wildlife & Wild Spaces, and The Human Journey. More than 50,000 comments have been added to 10,000 posts. Explore the list alongside to dive deeper into some of the most popular categories of the National Geographic Society’s conversation platform Voices.

Opinions are those of the blogger and/or the blogger’s organization, and not necessarily those of the National Geographic Society. Posters of blogs and comments are required to observe National Geographic’s community rules and other terms of service.

Social Media

About the Blog

Researchers, conservationists, and others share stories, insights and ideas about Our Changing Planet, Wildlife & Wild Spaces, and The Human Journey. More than 50,000 comments have been added to 10,000 posts. Explore the list alongside to dive deeper into some of the most popular categories of the National Geographic Society’s conversation platform Voices.

Opinions are those of the blogger and/or the blogger’s organization, and not necessarily those of the National Geographic Society. Posters of blogs and comments are required to observe National Geographic’s community rules and other terms of service.